Susan could be right in that it might be 2-4D or Banvel damage if
applied nearby.
One other possibility is a type of oak gall that Pin Oaks get. I'm not
sure, but I think it has to do with some sort of wasp. Nevertheless, the
leaves appear in a bulbous form, like a round green marble, and stay
that way through the year. We had one in our yard that the nursery
sprayed every spring before leafing out yet some leaves would still show
some symptoms. Finally I quit having them spray it and started using a
systemic insecticide via a Ross root feeder. It seemed to work.
Eventually the tree grew out of it as I was told it would. I can't
believe that there wasn't a lot of growth rate lost during the earlier
years due to the mishapen leaves.